Kieran, the Driven

First Strike, Menace
Whenever Kieran, the Driven attacks, you may. sacrifice another Bard you control. If you do, search your library for another Bard, reveal it, and put it into your hand. Kieran deals damage to any target equal to the sacrificed creature's power.
{u}{b}{r},{t}: Return target Bard from a graveyard to the battlefield under your control with a -1/-1 counter on it.